My Cleric had THACO of -1. Then he buffed up with Holy Power and he had THACO of -11. Then he casted Harm and suddenly his THACO went back to somewhere around 0. Why?

the only possible reason i can think of is because the -11/-1 thaco's are when you have a weapon equipped(the profiency point results in -1 thaco instead of the 0), harm is a spell, so HP doesnt effect it, and since you cant have a profiency point in it, you get the base THAC0...

But Holy Power sets the base THAC0 to be that of a Warrior of the same level. Apparently, Harm overrides it. Question: After casting Holy Power + Harm, and then using the Harm, does your THAC0 go back to -11?